590 research outputs found
Evidence against strong correlation in 4d transition metal oxides, CaRuO3 and SrRuO3
We investigate the electronic structure of 4d transition metal oxides, CaRuO3
and SrRuO3. The analysis of the photoemission spectra reveals significantly
weak electron correlation strength (U/W ~ 0.2) as expected in 4d systems and
resolves the long standing issue that arose due to the prediction of large U/W
similar to 3d-systems. It is shown that the bulk spectra, thermodynamic
parameters and optical properties in these systems can consistently be
described using first principle approaches. The observation of different
surface and bulk electronic structures in these weakly correlated 4d systems is
unusual.Comment: 4 pages, 4 figure
An Altered Derivatives Marketplace: Clearing Swaps Under Dodd-Frank
Though over a year has passed, the impact of the Dodd Frank Act remains unclear. This Note examines the provisions of the Act that relate to swap transactions within the context of pre-reform and postreform markets. In order to reduce the uncertainties inherent in unregulated swap transactions, the Act employs a comprehensive framework, which includes mandatory clearing through derivative clearing organizations, extensive reporting requirements, margin requirements, and position limits. This Note argues that, in doing so, the Dodd Frank Act addresses the fundamental failures of pre-reform derivative markets. However, the importance of the role for derivative clearing organizations under this framework creates a risk that these organizations will become systemically significant, mirroring problems with under-capitalized and over-exposed financial institutions in the downturn
Diagnostic Performance of PET Imaging Using Different Radiopharmaceuticals in Prostate Cancer According to Published Meta-Analyses.
A significant number of meta-analyses reporting data on the diagnostic performance of positron emission tomography (PET) in prostate cancer (PCa) is currently available in the literature. In particular, different PET radiopharmaceuticals were used for this purpose. The aim of this review is to summarize information retrieved by published meta-analyses on this topic. The first step included a systematic search of the literature (last search date: June 2020), screening two databases (PubMed/MEDLINE and Cochrane Library). This combination of key words was used: (A) "PET" OR "positron emission tomography" AND (B) "prostate" OR "prostatic" AND (C) meta-analysis. Only meta-analyses on Positron Emission Tomography/Computed Tomography (PET/CT) or Positron Emission Tomography/Magnetic Resonance (PET/MR) in PCa were selected. We have summarized the diagnostic performance of PET imaging in PCa, taking into account 39 meta-analyses published in the literature. Evidence-based data showed the good diagnostic performance of PET/CT with several radiopharmaceuticals, including prostate-specific membrane antigen (PSMA)-targeted agents, radiolabeled choline, fluciclovine, and fluoride in restaging and staging settings. Less evidence-based data were available for PET/MR with different radiotracers. More prospective multicentric studies and cost-effectiveness analyses are warranted
Disentangling coordination and alloy effects in transition metal nanoalloys from their electronic structure
International audienc
Inelastic transport theory from first-principles: methodology and applications for nanoscale devices
We describe a first-principles method for calculating electronic structure,
vibrational modes and frequencies, electron-phonon couplings, and inelastic
electron transport properties of an atomic-scale device bridging two metallic
contacts under nonequilibrium conditions. The method extends the
density-functional codes SIESTA and TranSIESTA that use atomic basis sets. The
inelastic conductance characteristics are calculated using the nonequilibrium
Green's function formalism, and the electron-phonon interaction is addressed
with perturbation theory up to the level of the self-consistent Born
approximation. While these calculations often are computationally demanding, we
show how they can be approximated by a simple and efficient lowest order
expansion. Our method also addresses effects of energy dissipation and local
heating of the junction via detailed calculations of the power flow. We
demonstrate the developed procedures by considering inelastic transport through
atomic gold wires of various lengths, thereby extending the results presented
in [Frederiksen et al., Phys. Rev. Lett. 93, 256601 (2004)]. To illustrate that
the method applies more generally to molecular devices, we also calculate the
inelastic current through different hydrocarbon molecules between gold
electrodes. Both for the wires and the molecules our theory is in quantitative
agreement with experiments, and characterizes the system-specific mode
selectivity and local heating.Comment: 24 pages, 17 figure
Telemedicine as a Medical Examination Tool During the Covid-19 Emergency: The Experience of the Onco-Haematology Center of Tor Vergata Hospital in Rome
Background: Our study analysed the outpatient activity of the onco-hematology Complex Operative Unit (UOC) of Tor Vergata Hospital, Rome coronavirus disease 2019 (Covid-19) center, where, as a result of the sudden and unexpected emergency, healthcare services were provided through telemedicine procedures that can be considered very close to Telehealth. Aim of the study: our retrospective study aimed to assess the widespread use of telemedicine in terms of feasibility and safety related to adverse events, a crucial experience which will make it possible to predict any effective use of such a method in patients with hematological disorders even after the end of the Covid-19 emergency. Materials and methods: At the Day Hospital clinic, from 8 March to 31 May 2020, an outpatient group received 3828 medical teleconsultations and 11,484 additional contacts following the first examination; each patient examined through the telematic method required an average of three supplementary contacts via e-mail or telephone. Results: The follow-up lasted 145 days, and all the events that occurred were monitored. In total, we recorded 16 clinical adverse events, 5 of which classified as major events, and 11 as minor events. Conclusion: The 3828 telematic clinical examinations and the 11,484 additional contacts following the first examination carried out by the onco-haematology UOC of Tor Vergata Hospital, proved how telemedicine, albeit in its basic form, was a key tool in facing the sanitary emergency caused by the sudden spread of Covid-19. An experience that can be considered reliable enough to be replicated in possible post-Covid-19 emergencies. From a medical forensic point of view, the main issues to consider are informed consent, personal data management and professional responsibility profiles
Lattice Distortion and Magnetism of 3d- Perovskite Oxides
Several puzzling aspects of interplay of the experimental lattice distortion
and the the magnetic properties of four narrow -band perovskite oxides
(YTiO, LaTiO, YVO, and LaVO) are clarified using results of
first-principles electronic structure calculations. First, we derive parameters
of the effective Hubbard-type Hamiltonian for the isolated bands using
newly developed downfolding method for the kinetic-energy part and a hybrid
approach, based on the combination of the random-phase approximation and the
constraint local-density approximation, for the screened Coulomb interaction
part. Then, we solve the obtained Hamiltonian using a number of techniques,
including the mean-field Hartree-Fock (HF) approximation, the second-order
perturbation theory for the correlation energy, and a variational superexchange
theory. Even though the crystal-field splitting is not particularly large to
quench the orbital degrees of freedom, the crystal distortion imposes a severe
constraint on the form of the possible orbital states, which favor the
formation of the experimentally observed magnetic structures in YTiO,
YVO_, and LaVO even at the HF level. Beyond the HF approximation, the
correlations effects systematically improve the agreement with the experimental
data. Using the same type of approximations we could not reproduce the correct
magnetic ground state of LaTiO. However, we expect that the situation may
change by systematically improving the level of approximations for dealing with
the correlation effects.Comment: 30 pages, 17 figures, 8 tables, high-quality figures are available
via e-mai
Fermi Surface and Electron Correlation Effects of Ferromagnetic Iron
The electronic band structure of bulk ferromagnetic iron is explored by
angle-resolved photoemission for electron correlation effects. Fermi surface
cross-sections as well as band maps are contrasted with density functional
calculations. The Fermi vectors and band parameters obtained from photoemission
and their prediction from band theory are analyzed in detail. Generally good
agreement is found for the Fermi surface. A bandwidth reduction for shallow
bands of ~ 30 % is observed. Additional strong quasiparticle renormalization
effects are found near the Fermi level, leading to a considerable mass
enhancement. The role of electronic correlation effects and the electronic
coupling to magnetic excitations is discussed in view of the experimental
results.Comment: 12 pages, 14 figures, 1 tabl
Study of Phase Stability in NiPt Systems
We have studied the problem of phase stability in NiPt alloy system. We have
used the augmented space recursion based on the TB-LMTO as the method for
studying the electronic structure of the alloys. In particular, we have used
the relativistic generalization of our earlier technique. We note that, in
order to predict the proper ground state structures and energetics, in addition
to relativistic effects, we have to take into account charge transfer effects
with precision.Comment: 22 pages, 7 figures. Accepted for publication in JPC
Effect of electronic doping and traps on carrier dynamics in tin halide perovskites
Tin halide perovskites have recently emerged as promising materials for low band gap solar cells. Much effort has been invested on controlling the limiting factors responsible for poor device efficiencies, namely self-p-doping and tin oxidation. Both phenomena are related to the presence of defects; however, full understanding of their implications in the optoelectronic properties of the material is still missing. We provide a comprehensive picture of the competing radiative and non-radiative recombination processes in tin-based perovskite thin films to establish the interplay between doping and trapping by combining photoluminescence measurements with trapped-carrier dynamic simulations and first-principles calculations. We show that pristine Sn perovskites, i.e. sample processed with commercially available SnI2 used as received, exhibit extremely high radiative efficiency due to electronic doping which boosts the radiative band-to-band recombination. Contrarily, thin films where Sn4+ species are intentionally introduced show drastically reduced radiative lifetime and efficiency due to a dominance of Auger recombination at all excitation densities when the material is highly doped. The introduction of SnF2 reduces the doping and passivates Sn4+ trap states but conversely introduces additional non-radiative decay channels in the bulk that fundamentally limit the radiative efficiency. Overall, we provide a qualitative model that takes into account different types of traps present in tin-perovskite thin films and show how doping and defects can affect the optoelectronic properties
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